1. Field of the Invention
The present invention relates to a liquid crystal display device and its fabrication method, and more particularly, to a liquid crystal display device with a passivation layer favorable for a printing method and its fabrication method.
2. Discussion of the Related Art
A display device, especially, a flat panel display device such as a liquid crystal display device, has an active device, such as a thin film transistor, in each pixel to drive the pixel. This kind of driving method of the display device is usually called an active matrix driving method. In such an active matrix method, the active device to drive the pixel is disposed at pixel regions arranged in a matrix form.
FIG. 1 is a view illustrating an active matrix liquid crystal display device. The liquid crystal display device in this figure is a TFT-LCD (Thin Film Transistor Liquid Crystal Display) employing thin film transistors as the active devices.
As illustrated in FIG. 1, perpendicularly arranged gate lines 2 and data lines 4 define pixel regions. A thin film transistor 10 is formed at the crossing point of the gate line 2 and the data line 4 to independently control driving of each pixel region. The thin film transistor 10 includes a gate electrode 2a connected to the gate line 2, a semiconductor layer 5 formed on the gate electrode 2a and activated when a scan signal is applied to the gate electrode 2a, and source/drain electrodes 4a and 4b formed on the semiconductor layer 5a. 
A pixel electrode 7 is formed at the pixel region and connected to the drain electrode 4b. When an image signal is applied to the pixel electrode 7 through the source and drain electrode 4a and 4b as the semiconductor 4 is activated, an image signal is applied to the pixel electrode 7 through the source/drain electrodes 4a and 4b to operate liquid crystal (not shown). The pixel electrode 7 is connected to the drain electrode 4b through a drain contact hole 8a. 
A storage electrode 6 is independently formed on the gate line 2, and a gate insulation film (not shown) is interposed between the gate line 2 and the storage electrode 6. The gate line 2 overlapping with the storage electrode 6 forms a storage capacitor Cst with the gate insulation film formed between the storage electrode 6 and the gate line 2, and the storage electrode 6 is connected to the pixel electrode 7 through the storage contact hole 8b. 
The storage capacitor Cst charges a gate voltage while a gate signal is applied to the gate electrode 2a and discharges the charged voltage while a data voltage is supplied to the pixel electrode 7 when the next gate line is driven, thereby preventing voltage change in the pixel electrode 7.
FIG. 2 illustrates a structure of a section taken along line I-I′ of FIG. 1 of the thin film transistor 10 and the storage capacitor Cst disposed in the pixel.
As illustrated, the thin film transistor 10 includes a substrate 1 made of a transparent insulation material such as glass; a gate electrode 2a formed on the substrate 1; a gate insulation layer 13 deposited over the entire substrate 1 with the gate electrode 2a formed thereon; a semiconductor layer 5a formed on the gate insulation layer 13 and activated as a signal is applied to the gate electrode 2a, an ohmic contact layer 5b formed on the semiconductor layer 5a, source/drain electrodes 4a and 4b formed on the ohmic contact layer 5b, and a passivation layer 15 formed on the source/drain electrode 4a and 4b to protect the TFT, on which a pixel electrode 7 is formed connected to the drain electrode 4b through the drain contact hole 8a. The source/drain electrodes 4a and 4b are electrically connected to the pixel electrode 7 formed in the pixel region, so that as a signal is applied to the pixel electrode 7 through the source/drain electrodes 4a and 4b, liquid crystal in the pixel region is driven to display an image.
Meanwhile, the storage capacitor Cst consists of the gate line 2, the storage electrode 6 and the gate insulation film 13 formed therebetween.
The passivation layer 15 is formed over the entire surface of the substrate 1 including the thin film transistor 10 and the storage electrode 6. Contact holes 8a and 8b are formed in the passivation layer 15 to expose portions of the drain electrode 4b and the storage electrode 6. The drain electrode 4b and the storage electrode 6 are electrically connected to the pixel electrode 7 through the contact holes 8a and 8b. 
The liquid crystal display device constructed as described above has the following problems.
That is, the liquid crystal display device is fabricated by a photomasking process including a series of photoresist deposition, alignment, exposure, development and cleansing. Also, plural photomasking processes are necessary to complete the liquid crystal display device, thus degrading a productivity.
In addition, in forming the contact hole of the passivation layer, after the photoresist is exposed, the photoresist is not completely removed during the developing process. The residual photoresist film causes an increase in contact resistance between the drain electrode and the storage electrode that are electrically connected to the pixel electrode, degrading a picture quality.